The invention relates generally to internal combustion engines and, more particularly, relates to an engine having a nonadjustable throttle linkage and to a nonadjustable throttle linkage usable on such an engine. The invention additionally relates to a method of mounting a nonadjustable throttle linkage on an engine.
Most engines employ a throttle to modulate airflow to the engine""s air intake valve(s) and possibly to advance ignition timing on demand. In the case of a carbureted engine, the throttle usually varies the position of a carburetor""s butterfly valve. In the case of a fuel injected system, each cylinder may have a dedicated throttle plate that can be pivoted to control airflow to the air intake valve(s) of that cylinder. All of the throttle plates of a particular row of cylinders of this type of engine are pivoted via a common throttle shaft that connects the throttle plates to one another. Hence, a V-6 or V-8 engine contains two throttle shafts, each of which controls the throttle plates of three or four cylinders. The throttle shafts are interconnected so as to rotate simultaneously and commensurately with one another. The throttle shafts are rotated by a throttle linkage that is connected to the throttle shafts via an output element for the throttle linkage. The throttle linkage includes a lever assembly that is connected to the output element and to an input element that is actuated either directly or indirectly by the engine""s operator.
Some throttle linkages include an idle stop and/or a fall-open stop to limit the operating range of the linkage""s lever assembly and, therefore, the engine operating speed range. In one configuration having both an idle stop and a full-open stop, both stops include a stop screw threaded into a throttle lever of the lever assembly. A head or jam nut of each stop screw engages a stationary seat when the throttle lever assembly is in the relevant position. The spacing of the jam nuts from the lever assembly can be varied to set and/or adjust the idle position and the fall-open position of the lever assembly.
The ability to vary the position of the jam nut of the stop screw of the throttle linkage relative to the linkage""s lever assembly produces marked drawbacks. For instance, the idle stop screw and full-open stop screw must be set upon initial assembly of each engine using a somewhat complex procedure that accompanies a throttle plate synchronization procedure. Specifically, after the throttle linkage is mounted on the engine and initially linked to the throttle shafts via the output element, the positions of both the idle stop screw and the full-open stop screw must be adjusted to assure that a cam roller of the output element rolls freely along the associated cam follower throughout the full range of lever assembly movement. This setting operation is usually an iterative process, considerably lengthening the time required to assemble an engine and running the risk of improper setting.
Settable or adjustable idle and wide-open stop screws are also prone to tampering by the engine""s operator. This tampering risks jamming or damage to some components of the throttle linkage if either stop screw is moved beyond a position in which the cam roller of the output element rides freely. Positioning either stop screw at a location other than the manufacturer""s recommended position also risks degraded engine performance and elevated emission levels. These problems are especially acute with respect to fuel injected outboard marine engines, which are subject to relatively onerous performance and emission requirements and which are often operated by individuals who like to tinker with the engine in an attempt to obtain a perceived enhanced performance.
Another problem associated with adjustable stops is that, if they are configured to be easily adjustable, they often tend to work loose from their preset positions due to vibrations resulting from engine operation. Their positions therefore must be periodically adjusted.
The need therefore has arisen to provide a throttle linkage for an engine, such as a fuel-injected outboard marine engine, that is not adjustable.
In accordance with a first aspect of the invention, a throttle linkage is provided that includes a lever assembly that is configured to connect an operator-manipulated input element to an output element that controls a throttle and possibly other components of the engine. The lever assembly typically includes at least two throttle levers, possibly coupled to one another by one or more links. At least one stop pin is mounted on the lever assembly and is configured to engage a stationary seat when the lever assembly is in one of a fall-open position and an idle position. One throttle linkage constructed in accordance with the invention has two stop pins, one of which engages an associated stationary seat when the lever assembly is in its full-open position, and the other of which engages an associated stationary seat when the lever assembly is in its idle position. The stop pins are axially locked with respect to the lever assembly so as to be axially nonadjustable relative to it. As a result of this arrangement, the operating stroke of the lever assembly is preset upon initial assembly of the throttle linkage and cannot be adjusted. This relationship significantly accelerates engine assembly and prevents tampering with the throttle linkage by the operator after the engine is assembled. It also prevents the stop pins from working loose during engine operation, negating the need to adjust the stop pins""positions.
Several techniques are available for axially locking a stop pin in position on the lever assembly. For instance, the stop pin could be swaged onto the associated component of the lever assembly. Alternatively, it could be screwed into the associated lever assembly component to a position in which a shoulder or other surface on the stop pin engages a lug or other seat on the lever assembly. In this case, measures are preferably taken to prevent or at least discourage post-assembly unscrewing of the stop pin from the associated component of the lever assembly. For instance, a cap could cover the head of the stop pin. A chemical locking agent could also be applied to the threads of the stop pin to inhibit the stop pin from unscrewing from the lever assembly due to vibrations imposed on the throttle linkage during engine operation. Tampering with a threaded stop pin could also be discouraged by threading the stop pin into the associated component of the lever assembly from the side that faces the associated stationary seat, thus preventing access to the head of the stop pin by a tool without removing the throttle linkage from the engine.
In accordance with another aspect of the invention, an internal combustion engine is provided that incorporates a nonadjustable throttle linkage of the type having at least some of the characteristics of the throttle linkage described above. In an application, such as an outboard marine engine, in which the engine extends vertically, the throttle linkage extends vertically along the side of the engine. An outboard marine engine presents a particularly beneficial application of the inventive throttle linkage because outboard marine engines are subject to rigid emission and performance standards and rather severe vibrations.
In accordance with yet another aspect of the invention, a simplified method is provided for mounting a throttle linkage on an internal combustion engine so as to facilitate engine assembly and to prevent post-assembly tampering with the throttle linkage. The method includes mounting at least one stop pin on a lever assembly so as to prevent subsequent axial adjustment of the stop pin relative to the lever assembly. Then, the lever assembly is mounted on the engine so that the stop pin faces a stationary seat on the engine so as to engage that stationary seat when the lever assembly is pivoted into one of its idle and full-open positions.
The stop pin may be mounted on the lever assembly by turning a head of the stop pin with a tool to screw a threaded portion of the stop pin into a correspondingly threaded portion of the lever assembly. Due to the orientation of the throttle linkage on the engine, the head of the stop pin faces and is adjacent to the stationary seat, thereby preventing or at least inhibiting access to the head of the stop pin by the tool. A cap may also be mounted over the head of the stop pin both to protect the stop pin and stationary seat and to further discourage tampering with the stop pin. Alternatively, the stop pin could be swaged onto the associated component of the lever assembly.
These and other advantages and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.